The peripheral arterial chemoreceptors located in the carotid body are sensitive to changes in partial pressure for oxygen and carbon dioxide in arterial blood. Initial hypoxia releases dopamine from glomus cells without altering the norepinephrine stores. Similarly, muscarinic receptor agonists elicit a release of dopamine but not norepinephrine. Methyl-atropine prevented the release of dopamine elicited by hypoxia or muscarinic receptor agonists. Long-lasting exposure to hypoxia or injection of carbohydrate-active steroids causes an increase in dopamine and norepinephrine content in cartoid body. These data suggest that the catecholamine content may be regulated hormonally and neuronally.